Preparation of mono-nu-alkylbenzenes by treating benzene and poly-nu-alkylbenzenes with hf-bf3



A. P. LIEN ETAL July 3, 1956 PREPARATION OF MONO-NALKYLBENZENES BY TREATLNG BENZENE AND POLYNALKYLBENZENES WITH HI -BF:

Filed Aug. 27, 1952 Arf/mr P. Lien David A. McCau/ay United States Patent PREPARATION OF MGNU-N-ALKYLBENZENES BY TREATING BENZENE AND POLY-N-ALKYLBEN- ZEN ES" -WITH l-iF-BFF.

ArthurP; Lien, Highland, Ind, and David A. McCaulay,

Chicago, Ill.*, assignorsto Standard Oil Company, Chicago, Ills, a corporation oflndiana Application August 27, 1952, Serial No. 306,648

6 Claims. (Cl; 260 -668) Broadly this invention relates to the transfer Of n-aIkyl groups, which are substituents of a. benzene ring, without isomerizingthe' alkyl group. Particularly this invention'relates to the preparation of a mono-n-alkylbenzene, wherein said alkylgroup contains three carbon atoms, by the interaction of corresponding poly-n-alkylbenzenes and benzene.

Some commercial demand has arisen for alkylbenzeneswherein the alkyl group contains three ormore carbon atoms which have anormal configuration of the alkyl group; e. g., mono-n-propylbenzene is of interestas a source of p-methylstyrene. Various methods are known for the alkylation of benzene; with n-alkyl halides to produce a mixture of mono-n-alkylbenzene and polyn-alkylbenzenes. However, attempts to convert said poly-n-alkylbenzenes to the corresponding mono-n-alkylbenzene invariably result in asubstantial isomerization of the alkyl group.v Thus preparation of mono-n-a kylbenzenes as presentlyv known involves low yields and substantial loss to side reactants, more or less unusable polyalkylbenzenes and less desirable iso-alkylbenzenes.

It is an. object of this invention to prepare mono-nalkylbenzene in high yield by the treatment of corresponding poly-n-alkylbenzenes. A particular object is the preparation of 'mono-n-propylbenzene by the interaction of a mixture ofpoly-n-propylbenzenes with benzene. Another object is thedisproportionation of monon-alkylbenzene to corresponding di-n-alkylbenzenes, par ticularly the meta-isomer thereof. Another particular object is the preparation of di-n-propylbenzenes, particularly meta-di-n-propylbenzene, in high yield by the disproportionation of mono-n-propylbenzene. Other objects of the invention will become apparent in the detailed description.

It has been discovered that poly-n-alkylbenzenes wherein the alkyl group contains three carbon atoms, and particularly the di-n-alkylbenzenes, can be converted in high yield to the corresponding mono-n-alkylbenzene by interaction with benzene in the presence of liquid HF and E1 3 at a temperature between about 0 and 120 F. The, amount of benzene present in the reaction zone is at'least about 1 mol for each .mol of alkyl groups that could'be transferred from said poly-n-alkylbenzenes to form'the corresponding mono-n-alkylbenzene. The liquid HF is present in an amount of at least about 3 mols per mol of alkylbenzenes in said feed to the reaction zone. The amount of BF3 present is less than about 1 mol per mol of said polyalkylbenzenes in said feed mixture. The reaction is carried on for a time suflicient to produce an appreciable amount of mono-n-alkylbenzene or may be carried on until an equilibrium. mixture is reached in the hydrocarbon product of the reaction.

The. liquid. HF used in the process of this invention may be used, e. g., 50-mols.

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shouldinot contain more than about 2..or 3% of water, i. e., the liquid HF should' be substantially. anhydrous. In order to eliminate the formation of undesired'BFahydrates, the process should becarriedout under substantially anhydrous conditions.

The amount ofliquid HF- treating agent used'in: the interaction process between poly-n alkylbenzenes and benzene should be at least about 3 mols per mol of :polyal'kylbenzenes in the feed'mixture. More than this=an iount It is preferredtto' useebetween' about and 300 volume percent of Fliq-uidHF, based-on said, feed mixture.-

In the interaction process the amount of BF3 present in-the reaction-zone mustbe less'than' about 1 mol per mol of said poly-n-alkylbenzenes in-saidfeed'm ixture, and preferablyleas than about 0.8 rnols. While amounts of BFs less than 0.2 mol may be used, it-is preferred'wto usebetween about 0.2 and 0.8 mol-per-molofsaidfeed poly-n-alkylbenzenes. 1

It has beenfound that the temperature-at which the process ofthis .invention iscarried"out-determines not only the rate of conversion to the desired .produet but also the amount of undesired product formed. Thei-term undesired product includes not. only. alkylbenzenes wherein the alkylgroup has a configuration other than the normal configuration, e. g.,-iso-, sec-, tert-, but also poly-.n-alkylbenzenes having fewer. carbon atoms in-the alkyl group-than were present in the. feed to the process. In order to substantially eliminate these. undesireds side reactions, particularly the isomerization of thevalkyl group itself, the reaction temperature of this inventionismaintained below about F. Temperatures as low as -0 may be used if correspondingly longerreaction times can be tolerated. In the interaction processit is-preferredto operate at a temperature between about. 60 and 100 F. and maintain saidreaction for a-time sufiicient toproduce eitheran equilibrium product mixture or-the desired degree of conversion lower than vtheequilibrium composition.

The feed to .the interaction process ofthis invention may be anypoly-n-alkylbenzene wherein the alkyl group contains three carbon atoms, e. g., di-n-propylbenzene. Particularly suitable feed stocks to this interaction. process are di-n-propylbenzene. and tri-n-propylbenzene. Also the feed stock to the interaction process may be the reaction product of an alkylation process for the manufacture of mono-n-propylbenzene. The alkylation'. of benzene with n-propyl chloride, .using FeCla as the-cataly st orusing AlCl at temperatures below about 0C., produces a mixture of mono-n-propylbenzene, di-n-propylenzenes and tri-n-propylbenzenes. The term feed consisting essentially of poly-n-alkylbenzenes is intended to include such natural mixtures of the mono, di and .tri-npropylbenzenes.

It has been found that the interaction process should becarried out in the substantial absence of aromatic hydrocarbons other than the poly-n-alkylbenzenes and benzene. Furthermore, the presence of appreciable amounts of non-aromatic hydrocarbons such as paraffins and naphthenes has a deleterious effect on the degree of conversion. The feed mixture should not contain amounts of other aromatic hydrocarbons and non-aromatichydrocarbons beyond those amounts normally present as impurities in commercial grade benzene and polyn-alkylbenzenes.

The interaction process involves equilibrium reaction and it has been found that the amount of benzene present in the reaction zone influences the degree of conversion to the desired mono-n-alkylbenzene. For convenience the amount of benzene used is related to the alkyl groups that could be transferred from the feed polyalkylbenzene to a benzene molecule to form the desired mono-n-alkylbenzene product. In general the amount of benzene added should be equal to at least about one benzene molecule for each alkyl group that could be transferred; or put in another way: about 1 mol of henzene for each mol of alkyl groups that could be transferred. Somewhat less than this amount of benzene can be used where the degree of conversion is not of paramount impartance. It is preferred to use considerably more than about 1 mol of benzene, e. g., between about 3 and 10 mols of benzene per mol of alkyl groups that couldbe transferred. Thus when operating on di-n-propylbenzene, the amount of benzene present in the reaction zone should be about 1 mol per mol of di-n-propylbenzene in the feed, and preferably should be between about 3 and 10 mols per mol of di-n-propylbenzene in the feed.

When operating under the above-described conditions, a mixture of aromatic hydrocarbons, i. e., hydrocarbon products, is obtained along with HF and BFs. The hydrocarbon products consist essentially of unreacted benzene, unreacted feed poly-n-alkylbenzene and product mono-n-alkylbenzene. These materials are readily sep arated by fractional distillation and the unreacted benzene'and poly-n-alkylbenzenes can be recycled to the reaction zone.

It has also been discovered that mono-n-alkylbenzenes can be disproportionated to a mixture of di-n-alkylbenzenes, which mixture is predominantly the meta-isomer or substantially completely meta-isomer by contacting said mono-n-alkylbenzene with liquid HF and BF3, at a temperature between about and 120 F. for a time sufficient to produce an appreciable amount of the desired di-n-alkylbenzene. The amount of liquid HF should be at least about 2 mols per mol of said feed alkylbenzene. The amount of BF: is at least about 0.3 mol per mol of said-alkylbenzene and preferably about 0.5 mol.

' The amount of liquid HF used in the disproportionation'process should be at least about 2 mols and may be as high as 50 mols per mol of feed mono-n alkylbenzene.

' It'is preferred to use between about 100 and 300 volume percent of liquid HF, based on feed to the process.

The amount of BFs used in the disproportionation process is important in order to obtain an appreciable degreeof conversion. It has been found that at least about 0.3 mol of BFs per mol of feed mono-n-alkylbenzene must be used in order to obtain appreciable amounts of the corresponding di-n-alkylbenzenes. By the use of 0.5 mol of BFs per mol of feed mono-n-alkylbenzene. very high yields of di-n-alkylbenzenes are obtained; and this with substantially no higher n-alkylbenzenes such as tri-n-alkylbenzenes. It has been found that the di-n-al 'kylbenzenes are predominantly the meta-isomer and that under proper conditions of temperature, contact time and the use of about 0.5 mol of BFs per mol of feed mono-n-alkylbenzene, the product di-n-alkylbenzene consists' essentially of the meta-isomer.

In order to substantially eliminate the isomerization of the alkyl group and cracking reactions when operating with longer chain alkyl groups, the temperature of the reaction should be held below about 120 F. While the temperature of the disproportionation reaction may be between about 0 and 120 B, it is preferred to operate between about 40 and 100 F. in order to substantially eliminate side reactions and to obtain reasonable contact times with a high degree of conversion to the del sired product.

Particularly suitable feed stocks to this reaction are mono-n-propylbenzene and mono-n-butylbenzene. It

has been found that the presence of other aromatic bydrocarbons, particularly benzene and toluene, has an adverse elfect on the degree of conversion and the hydrocarbon products obtained. Also, the presence of nonaromatic hydrocarbons such as paraflins and naphthenes is undesirable. it is preferred to operate on a feed that contains no more than the commercial amounts of impurities such as non-aromatic hydrocarbons and other aromatic hydrocarbons.

The annexed drawing which shows schematically an illustrative embodiment of a process for utilizing this invention is a part of this specification. It is to be understood that th illustrative embodiment omits many items of process equipment such as pumps and valves, which items can be readily added thereto by one skilled in the art. Furthermore, many variations on this embodiment can be readily made by one skilled in the art. Such variations are included within the scope of the invention.

The illustrative embodiment shows the preparation of mono-npropylbenzene by the interaction of a mixture of diand poly-n-propylbenzenes with benzene. The diand poly-n-propylbenzenes are obtained as fractions of the product of the alkylation of benzene with n-propyl chloride, the other alkylate fraction being mono-n-propylbenzene when AlCls is used as the alkylation catalyst at a temperature of about -10 C. Thus by our process We are able to obtain a very high yieldof mono-npropylbenzene when it is operated in conjunction with such an alkylation process.

With reference to the drawing, the above mixture of diand poly-n-propylbenzenes from source 8 is passed through line 9 into line 13.

Benzene from source 11 ispassed by way of lines 12 and 9 into line 13. In this embodiment 5 mols of benzene are used per mol of transferable propyl groups present in said poly-n-alkylbenzene mixture.

Liquid HF from source 14 is passed by way of valved line 16, lines 17 and 18 into line 13. The amount of liquid HF used herein is 225 volume percent, based on the feed mixture in line 13.

Boron trifluoride from source 19 is passed by way of valved line 21 and lines 22 and 18 into line 13. In this illustration the amount of BF; used is 0.7 mol per mol of polyalkylbenzenes in said feed mixture.

The liquid HF, BE and feed in line 13 are passed into mixer 23, which mixer is provided with heat transfer coil 24. In mixer 23 the feed and the I-IF-BFa treating agent are thoroughly intermingled and the temperature thereof is raised to F. by means of heat transfer coil 24 and exothermic heat of reaction. The thoroughly intermingled materials are withdrawn from mixer 23 and passed through line 27 into reactor 28.

Reactor 2% is provided with heat exchange coil 29 and agitation means not shown. In reactor 28 the materials are maintained at a temperature of about 90 F. for a time of about 1 hour. At this temperature this reaction time results in the production of a substantially equilibrium mixture of mono-n-propylbenzene, poly-npropylbenzenes and benzene. The equilibrium mixture of monoand polypropylbenzenes consists of about 90% of the mono-n-propylbenzene.

The hydrocarbon product and HF-BFa treating agent are Withdrawn from reactor 28 and are passed through lines 30 and 32 into stripper 33. When it is desired to operate at about F. in order to obtain shorter reaction times, it may be desirable to cool the reaction mixture in order substantially to stop further reaction and thereby eliminate undesired side reaction products. This cooling is carried out in heat exchanger 31. In this illustration heat exchanger 31 is not used.

Stripper 33 is provided with internal heat exchanger 34. In stripper 33 the HF and 3P3 are removed from the hydrocarbon product by distillation, preferably in the presence of an added non-reactive stripping agent. Suitable stripping agents are low boiling paraffinic or eysassa naphthenic hydrocarbons, such as, propane, butane, pentane, cyclopropane, cyclopentane, etc. It is preferred to operate stripper 33 under vacuum in addition to using a stripping agent. In this embodiment butane is introduced at a low point of stripper 33 by Way 'of line 35. Butane, HF and BFs are withdrawn overhead from stripper 33 by way of line 36 through vacuum pump 37, line 38, heat exchanger 39 and line 41. v

Butane and HF are liquefied in heat exchanger 39. The contents of line '41 are passed into settler 42. An upper layer of liquid butane i's Withdrawn from settler 42 by way of line 46 and is recycled to line 35 for reuse in the stripping operation by way of lines not shown.

A lower layer of liquid HF saturated with BF3 is withdrawn from settler 42 by way of valved line 47 and is returned to the reaction zone by way of said line 47 and lines 17 and 18. Gaseous BB; is withdrawn from an upper portion of settler 42 and is passed by way of lines 43, 44, 22 and 18 to the reaction zone for reuse in the process.

No BFs purification step is shown herein. However, it may be desirable over a period of time to treat the BFs to remove non-condensible gases which are formed to some extent in the process and also to eliminate BFa hydrates from the system.

A hydrocarbon product is withdrawn from stripper 33 by way of line 51 and is passed through heat exchanger 52 and line 53 into fractionator 54. Fractionator 54 is provided with internal heat exchanger 55. Fractionator 54 is so constructed that it is possible to withdraw overhead through line 56 a benzene fraction, a bottoms fraction through line 57 which consists of unreacted poly-npropylbenzene and a product fraction through line 58. The benzene may be recycled to line 12 by way of lines not shown. The unreacted poly-n-propylbenzenes may be recycled to line 9 by way of valved line 59. The product fraction, which in this embodiment consists of substantially pure mono-n-propylbenzene, is passed to storage not shown.

The disproportionation of mono-n-alkylbenzene to din-alkylbenzenes can be carried out in a manner very similar to that described above. Of course no benzene would be added to the feed mono-n-alkylbenzene in the disproportionation process. From fractionator 54 an overhead benzene fraction would be obtained. However, the side stream of mono-n'alkylbenzene in line 58 would be recycled to the reaction zone while the bottoms fraction in line 57 would be sent to storage as the desired product di-n-alkylbenzene. The bottoms product in this embodiment of the disproportionation reaction will consist essentially of the meta-di-n-alkylbenzene.

The results obtainable with the processes of this invention are illustrated by the following examples:

The apparatus used in the illustrative test was a 1570 ml. carbon steel autoclave fitted with a 1725 R. P. M. mechanical stirrer. The desired amount of feed was charged to the reactor and the substantially anhydrous liquid HF was added. The BFa Was charged and the contents of the reactor were raised to the desired temperature and agitated for the desired contacting time. At the end of the contacting time the stirrer was stopped and the contents were allowed to settle for minutes.

Example I In this example substantially pure n-propylbenzene was disproportionated. This example was carried out using 125 ml. (about 6 mols) of liquid HF and 0.7 mol of BFs. The mono-n-propylbenzene charged was 300 ml. (2.16 mols). Thus the BFs was present in an amount of 0.32 mol per mol of feed mono n-propylbenzene. The contents of the reactor were agitated for 10 minutes at 40 F. and were allowed to settle for 10 minutes for phase separation before being withdrawn. The lower acid-rich phase and the upper rafiinate phase were treated sepa- 6 rately to recover hydrocarbon product. In this example 76 wt. percent of the total hydrocarbon product was recovered from the raflinate phase and 24 wt. percent of the hydrocarbon product was recovered from the extract phase. The hydrocarbon product distribution is shown below in mol percent for the two phases, respectively,

- and for the total product.

Compound Raifinate Extract Total Benzene 21 16 20 Mono-n-propylbenzene 66 34 60 rn-di-n-Propylbenzene. 13 44 19 Tri-n-propyl benzenes. None 6 1 Example 11 In this example di-n-propylbenzene, produced as in Example I, was interacted with benzene. The charge to the reactor in this example consisted of di-n-propylbenzone, .21 mol; benzene, 1.72 mols; liquid HF, 250 ml. (12.5 mols); and BFs, .15 mol. Thus the mol ratio of benzene to di-n-propylbenzene was 8.3. The mol ratio of BFs to di-n-pro-pylbenzene was 0.7. The contents of the reactor were agitated for 60 minutes at 73 F. and were settled for 10 minutes before being withdrawn from the reactor.

Analysis of the product hydrocarbons indicated that no detectable amounts of polypropylbenzenes higher than dipropylbenzenes had been formed. The propylbenzene product distribution showed that 22% of the charge di-npropylbenzene had been converted to mono-n-propylbenzene. Infrared analysis showed that within analytical accuracy no isomerization of the propyl group had occurred.

Thus having described the invention, what is claimed is:

1. A process for the production of mono-n-propylbenzene by the interaction of poly-n-propylbenzenes and benzone, which process comprises contacting, under substant1ally anhydrous conditions, a feed consisting essentially of poly-n-propylbenzene, and benzene, said benzene being present in an amount of at least one mole for each mole of propyl groups that could be transferred, with at least about 3 moles of liquid HF per mole of said feed propylbenzenes and with BF3 in an amount between about 0.2 and 0.8 mole per mole of said feed propylbenzenes at a temperature between about 0 and 120 F. for a time sufficient to produce an appreciable amount of mono-n-propylbenzene, recovering a hydrocarbon product by removing HF and BF3 therefrom and recovering mono-n-propylbenzene from said product.

2. The process of claim 1 wherein said feed polypropylbenzenes consist essentially of dim-propylbenzenes.

3. The process of claim 1 wherein said benzene is present in an amount between about 3 to 10 mols per mol of transferable propyl groups in said polypropylbenzenes.

4. The process of claim 1 wherein said liquid HF is present in an amount between about and 300 volume percent, based on said feed.

5. The process of claim 1 wherein said temperature is between about 60 and 100 F.

6. A process for the production of mono-n-propylbenzene by the interaction of di-n-propylbenzenes and benzene, which process comprises contacting a feed consisting essentially of di-n-propylbenzenes and benzene, wherein References Cited in the file of this patent between about 3 and 10 111015 of benzene are present per mol of di-n-propylbenzenes, with between about 3 and UNITED STATES PATENTS 50 mols of liquid HF based on said feed di-n-propylben- ,324,143 Bro ks et a1. Dec. 9, 1919 zene, and with between about 0.2 and 0.8 mol of BFa 5 2,194,449 h n n t a1 Mar. 19, 1940 per mol of said di-n-propylbenzenes, at a temperature be- ,3 ,524 MattOX Sept. 25, 1945 tween about 0 and 120 F. for a time sufficient to obtain 96,96 Pa ino Mar. 19, 1946 an appreciable amount of rnono-n-propylbenzene, re- 8 ,9 9 Lee et a1 Sept. 6, 1949 covering a hydrocarbon product by removing HF and 2 ,893 Lien et a1 W Nov. 7, 1950 BFs therefrom, and recovering said mono-n-propylben- 10 4, 72 S hulZe Dec. 12, 1950 zene vfrom said product. ,073 Lien ct a1 Aug. 14, 1951 

1. A PROCESS FOR THE PRODUCTION OF MONO-N-PROPYLBENZENE BY THE INTERACTION OF POLY-N-PROPYLBENZENES AND BENZENE, WHICH PROCESS COMPRISES CONTACTING, UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS, A FEED CONSISTING ESSENTIALLY OF POLY-N-PROPYLBENZENE, AND BENZENE, SAID BENZENE BEING PRESENT IN AN AMOUNT OF AT LEAST ONE MOLE FOR EACH MOLE OF PROPYL GROUPS THAT COULD BE TRANSFERRED, WITH AT LEAST ABOUT 3 MOLES OF LIQUID HF PER MOLE OF SAID FEED PROPYLBENZENES AND WITH BF3 IN AN AMOUNTT BETWEEN ABOUT 0.2 AND 0.8 MOLE PER MOLE OF SAID FEED PROPYLBENZENES AT A TEMPERATURE BETWEEN ABOUT 0* AND 120* F. FOR A TIME SUFFICIENT TO PRODUCE AN APPRECIABLE AMOUNT OF MONO-N-PROPYLBENZENE, RECOVERING A HYDROCARBON PRODUCT BY REMOVING HF AND BF3 THEREFROM AND RECOVERING MONO-N-PROPYLBENZENE FROM SAID PRODUCT. 